The explosive growth in the volume and variety of multi-media telecommunication applications continues to drive speed demands for internet traffic and motivate research in backbone fiber-optic communication links Coherent communications and electronic digital signal processing (DSP)-based receivers have been accepted in recent years as the next—generation standards for long-haul systems due to their flexibility, scalability and ability to compensate for various transmission impairments, including fiber nonlinearity.
However, the proposed DSP algorithms for nonlinearity mitigation are not anticipated to provide orders-of-magnitude performance improvements. Consequently, new transmission media and multiplexing/demultiplexing techniques may need to replace standard single-mode fibers to achieve transmission performance beyond what the DSP algorithms can provide.
To exploit the remaining capacity in optical fiber, advanced multi-level modulation formats, such as QAM, and/or superchannel OFDM systems will be needed. However these systems require higher signal-to-noise ratios (SNR) than are currently feasible. However these systems require higher signal-to-noise ratios (SNR) than are currently feasible. Fiber nonlinearities and fiber attenuation are the key performance limitations that prevent the higher SNRs from being achieved.
Another solution is needed to increase system capacity. Recent experiments have demonstrated that it is possible to transmit signals in more than one spatial propagation mode of a FMF using multiple-input multiple-output (MIMO) techniques. However, because of their relatively large effective areas, few moded fibers also have increased levels of attenuation, thus making it difficult to achieve the desired high power signal levels.